A segmented spherical primary mirror is an ideal candidate for a low-cost, large aperture optical telescope system. The use of inexpensive replication techniques for the segmented spherical mirror makes the system affordable. However, this results in a system that traditionally does not perform well, especially over a field of view. The Hobby-Eberly telescope system is an example of such a system.
Most well-corrected optical telescope systems use a primary mirror that has a parabolic or nearly-parabolic shape. A method that has been used recently in these systems to correct for aberrations in the pupil involves placing a deformable mirror at the exit pupil. The shape of the deformable mirror is changed via actuators behind a membrane optical surface. The problem is that for a continuous spherical primary mirror, the optical rays become unseparable at the pupil location. A deformable mirror at this location cannot correct aberrations introduced from a spherical primary mirror. Moreover, the pupil mirror does not correct for the discontinuity resulting from adjacent edges of a segmented mirror.
Increased interest in generating larger and larger optical telescopes for space and ground observatories points to the need for an improved, low-cost and high quality, optical telescope system. The present invention addresses this need. To this end, an optical telescope system according to the invention comprises a segmented primary mirror having a plurality of spherical mirror segments arranged in a non-spherical shape so that the rays incident upon the individual spherical mirror segments stay separated at an exit pupil of the telescope system, allowing for correction of aberrations. A discontinuous pupil corrector is located at the exit pupil of the telescope system. The discontinuous pupil corrector comprises a segmented mirror having a plurality of aspheric correction terms in it for correction of aberrations introduced from respective ones of the plurality of spherical mirror segments of the segmented primary mirror. In a disclosed, preferred embodiment of the invention, the system is a deployable, space optical telescope system.
A method of obtaining diffraction limited optical performance in a large aperture optical telescope system according to the invention comprises the steps of: providing a large aperture optical telescope system having a segmented primary mirror with a plurality of spherical mirror segments tilted and positioned to form a non-spherical shape so that rays incident upon the individual spherical segments stay separated at an exit pupil of the telescope system, allowing for correction of aberrations; reflecting rays incident upon the individual spherical segments of the primary mirror to the exit pupil of the telescope system; and correcting aberrations introduced into the reflected rays from respective ones of the plurality of spherical mirror segments of the primary mirror at the exit pupil of the telescope system using a discontinuous pupil corrector comprising a segmented mirror at the exit pupil having a plurality of aspheric correction terms in it in respective segments of the discontinuous pupil corrector mirror. The segmented mirror of the discontinuous pupil corrector in the disclosed embodiment preferably is a segmented deformable mirror.
The optical telescope system and method of the invention can achieve diffraction limited performance for very large systems while allowing inexpensive replication techniques to be used for making segments of the primary mirror. These and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the invention, including a preferred embodiment thereof.